Survival Analysis of COVID-19 Patients in South Korea

Sherly Boddu and Sam Hsu

4/21/2020

Outline

  1. Background: COVID-19 in South Korea
  2. Objectives: Understanding survival rates by age, sex, and province
  3. Methods: Cox proportional hazards regression
  4. Results
    1. Individual and geographic demographics
    2. Results from Cox proportional hazards model
  5. Discussion

COVID-19 in Korea

Risk Factors for Mortality

Korean Provinces

Objectives

Data Source

Analysis Plan

DAG

Statistical Analysis

The hazard function is the instantaneous risk of death at time \(t\), conditional on survival up to that time: \[h(t) = \lim_{\Delta t\rightarrow0} \frac{Pr[(t \leq T < t + \Delta t | T \geq t)]}{\Delta t}\]

Cox proportional-hazards model for relationship of survival distribution to covariates:

\[h_{i}(t) = h_{0}(t) \exp(\alpha + \beta_{sex}x_{i,sex} + \beta_{age}x_{i, age} + \beta_{province}x_{i, province})\]

Model Assumptions: Proportional Hazards

We assume proportional hazards. This is acceptable, using the cox.zph function to test.

Model Assumptions: No Influential Cases

We assume no influential cases. This does not hold at the province level, but in certain provinces only 1 or 2 deaths were recorded.

COVID-19 Clusters

Demographic Characteristics

Table 1: Characteristics of people diagnosed with COVID-19 in South Korea between 01/20/2020 and 04/20/2020 Full sample (N = 2,772) Deaths only (N = 65)
Sex:      
   Male 1,175 (43.3%) 44 (65.7%)
   Female 1,536 (56.7%) 23 (34.3%)
Age:      
   Mean (SD) 45.53 (20.68) 74.61 (13.08)
Province:      
   Busan 129 (4.7%) 3 (4.5%)
   Daegu 63 (2.3%) 20 (29.9%)
   Gangwon-do 37 (1.3%) 1 (1.5%)
   Gyeonggi-do 656 (23.6%) 1 (1.5%)
   Gyeongsangbuk-do 1,223 (44.1%) 39 (58.2%)
   Seoul 624 (22.5%) 2 (3.0%)
   Ulsan 42 (1.5%) 1 (1.5%)
Days to Resolution (Death or Release):      
   Mean (SD) 21.16 (9.75) 8.15 (10.10)
Disease State:      
   Deceased 67 (2.4%) 67 (100.0%)
   Isolated 1,438 (51.8%) 0 (0.0%)
   Released 1,269 (45.7%) 0 (0.0%)

Density Curve by Sex

Density Curve by Age

Density Curve by Province

Cox Results

Characteristic HR1 95% CI1 p-value
Sex
female
male 3.33 1.99, 5.57 <0.001
Age 1.08 1.06, 1.10 <0.001
Province
Busan
Daegu 11.3 3.30, 38.4 <0.001
Gangwon-do 1.52 0.16, 14.7 0.7
Gyeonggi-do 0.08 0.01, 0.73 0.026
Gyeongsangbuk-do 1.10 0.34, 3.62 0.9
Seoul 0.21 0.03, 1.26 0.087
Ulsan 2.13 0.22, 20.8 0.5

1 HR = Hazard Ratio, CI = Confidence Interval

Visualization of Cox Results

K-M by Sex

K-M by Age

K-M by Province

Key Results

Consistency

Strengths and Limitations

Strengths

Limitations

Future Directions

Questions?

References

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